It is important that an aircraft is designed so that its weight becomes as small as possible. However, an aircraft is very complicated and has many parts. Therefore, optimization of weight has been attempted when an outline specification is designed depending on performance required for the whole aircraft (for example, refer to Japanese Patent Application Publication JP 2013-073596 A).
When an outline specification of the whole airframe is determined so that its weight becomes as small as possible, a structural pattern and a structure diagram for every structural object, such as main wings and a fuselage, are determined according to the outline specification. For example, in the case of a main wing, a structural pattern, such as the number and arrangement of spars and ribs, is determined according to an outline specification of the whole airframe.
When a structural pattern of a structural object is determined, sizing (size determination) of sheet thicknesses, cross-sectional areas and the like of parts composing the structural object is performed. Specifically, a structural object is evaluated for each of various evaluation items, such as whether the structural object has necessary intensity and flutter speed, and sizing of each part is performed so that constraints are satisfied for all of the evaluation items.
An object of the present invention is to allow further reducing a weight of an aircraft.